The De Morgan law is detailed

I. De Morgan Law

Non (A and B) = (not a) or (not B)

Non (A or B) = (not a) and (not B)

1. De Morgan Law really makes people headache, the following for everyone specific

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a=1+2; b=2+3; c=4

Non-a=3+4

Non-b=1+4

A and B are both A and B at the same time, so a and b=2

A or B can be either A or B, so a or b=1+2+3

So not (A and B) =1+3+4 (not a) or (not B) =3+4+1

Not (A and B) = (not a) or (not B)

In the same vein, non (A or B) = (not a) and (not B)

(2) in Linux, the combined condition is

With:-A

Or:-O

Non:-not,!

De Morgan Law is:

! A-a! B =! (A-o B)

! A-o! B =! (A-a B)

Instance:

Look for the last week in the/var directory where its content has been modified and is not the root of the master, nor is it a postfix file

[Email protected] bin]# find/var-mtime-7-not \ (-user root-o-user postfix \) or [[email protected] bin]# find/var-m Time-7-not-user root-a-not-user postfix

Two. Operation:

1. Find the main root of the/var directory and all files belonging to the group Mail

[Email protected] bin]# find/var-user root-group Mail

2. Find all files in/var directory that do not belong to root, LP, GDM

[[email protected] bin]# find/var-not \ (-user root-o-user lp-o-user GDM \)-ls

3, find in the/var directory in the last week of its content has been modified, and the owner is not root, nor postfix files

[[email protected] bin]# find/var-mtime-7-not \ (-user root-o-user postfix \)

4. Find files that are not owned by the master or group on the current system and have been visited in the last week

[Email protected] bin]# Find/-nouser-nogroup-atime-7-ls

5. Find all files that are larger than 1M in the/etc directory and are of normal file type

[Email protected] bin]# find/etc-size +1m-type f-ls

6. Find files with no write permission for all users in/etc directory

[Email protected] bin]# find/etc/-not-perm/222-ls

7. Find at least one class of users who do not have permission to execute files in/etc directory

[Email protected] bin]# find/etc/-not-perm-111-ls

8, find/etc/init.d directory, all users have execute permission, and other users have write permission files

[Email protected] bin]# find/etc/init.d/-perm-113

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The De Morgan law is detailed